Experimental results reported in the literature indicate that
the advice often given to farmers in developing countries to wean
calves early in order to increase the amount of saleable milk is
inappropriate. Suckling can increase milk yields and may reduce
the incidence of mastitis, as well as prolonging lactation.
Calves allowed to suckle for limited periods are healthier and
grow faster than those reared on substitute milk feeds. Bos
indicus breeds and even their F1 crosses with European breeds
may not let down their milk unless stimulated by suckling their
calves briefly prior to hand or machine milking.

In his book "The Calf: Management and Feeding", Roy
(1970) states "In general, it will be more economic to wean
at the youngest age possible, commensurate with achieving a low
mortality and the desired weight gain". Similarly, Fishwick
(1962) writes 2Milk is an expensive food... and in commercial
herds it is desirable to reduce to a minimum the amount of whole
milk fed to calves. This can be done by using a milk
substitute."

Are these recommendations sensible from the point of view of
resource-poor farmers in developing countries? This paper briefly
reviews the main considerations, some of which were discussed by
Preston (1983).

Substitute milk foods

The practice of very early weaning and substitute feeding has
been developed in association with large dairy herds, managed in
conditions vastly different from the small units of most Third
World farmers. Substitute milk diets for calves are generally
based on dried skim milk, a by-product of large-scale butter
manufacture, the butterfat being replaced by such fats as lard,
tallow or coconut oil. Other ingredients may include hydrolysed
cereal starch, ground oilseeds, blood and bone flours, fishmeal
and antibiotics (Petersen 1950; Roy 1970).

The regular supply of a nutritionally adequate calf milk
replacer presupposes dependable sources of the various
ingredients and high technical skills and equipment for blending
them, e.g. for the homogenization and stabilization of fat.
Miller (1979) notes that "the requirements for a good milk
replacer are more rigorous than for any other type of food
normally used by cattle".

Above all, substitute feeding assumes that the farmer gains
enough from the sale of milk not drunk by the calf to pay for the
feed. Where ingredients are expensive because of scarcity or
transport over a long distance, this may not be possible.

The effect of suckling on milk yields

There is in fact much evidence from work carried out on
large-scale dairy farms to show that suckling can increase milk
production (Everitt et al 1968; Everitt and Phillips 1971;
Walsh 1974; Chandler and Robinson 1974; Laoser 1975; Peel et
al 1979; Thomas etal 1981; Copeman and
Phillips 1983; Perez et al 1984). These studies were
carried out on herds in New Zealand, Australia, Ireland and
France, their prime aim being to test the feasibility of rearing
three or four beef calves per cow, in order to utilize the milk
which is surplus to the requirements of creameries during the
season of maximum production. Estimates of milk yields - based on
the differences between the calves' weights before and after
suckling - exceeded the yields of control cows milked by machine.
Smith et al (1973), on the other hand, observed no
increase in milk fat production (milk weight was not recorded) by
cows grazing pasture during a period of drought, which suggests
that a low plane of nutrition may limit the capacity to respond
to suckling.

In several investigations, milk production by cows sucked for
up to 12 weeks continued to exceed that of control animals for
some time, even after weaning (Everitt and Phillips 1971; Veitia
and Simon 1972; Kaiser 1975; Fulkerson et al 1978; Peel et
al 1979).

The percent increase in post-weaning yield appears to depend
on the duration of suckling, a minimum of four weeks being
necessary for significant response (Peel et al 1979), but
no differences were found between cows which had been sucked for
6, 9 and 12 weeks (Kaiser 1975). When the cows were on a
restricted diet, there was no effect on post-weaning milk
production (Kaiser 1975), again suggesting that a minimum plane
of nutrition is necessary for the response.

Restricted suckling

The capacity to respond to suckling varies with the breed of
the cow. Ugarte and Preston (1972) compared pure Holstein with
Holstein x Brahmin F1 cows. They were either only milked or were
allowed to suckle their own calves for 15 to 30 minutes twice
daily, shortly after milking. In the Holsteins, the increase in
total milk production in response to suckling was 45%; in the
crossbreds, it was 73%. This work showed that, although the yield
of saleable milk may be reduced when the calf remains
continuously with its dam, restricted suckling twice daily can so
increase production that the quantity available for sale is
unchanged or even increased.

Paredes et al (1981), using Brown Swiss x Holstein cows
in a similar study, confirmed this. Their control group averaged
14 kg/day whereas the sucked cows on average gave 16 kg/day at
milking plus 5 kg/day taken by the calf.

The study of Ugarte and Preston (1972) is particularly
relevant to the needs of resource-poor farmers because, in some
of the trials, the cows were hand-milked. Since hand-milking
tends to empty the udder less completely than machine-milking and
since milk secretion is stimulated more when the udder is
thoroughly emptied, the effect of suckling after milking is
likely to be greater in hand-milked cows.

Possible effects of suckling on prolactin levels

The presence of the calf during lactation may have effects
additional to better udder evacuation. Tactile stimulation of the
udder and teats, by the calf or by hand, promotes the secretion
from the cow's pituitary gland of prolactin (Johke 1969; Tucker
1971; Kiprowski et al 1971; Reinhardt and Schams 1974).
The additional stimulus of suckling after milking increased
prolactin release in Friesian heifers (Fulkerson et al
1978). This extra stimulation may be even more effective in the
indigenous cattle of developing countries than in western dairy
breeds, which may have been selected unknowingly but effectively
for high prolactin release in response to relatively little
stimulation.

It is conceivable that, in some tropical breeds, the presence
of the calf triggers a reflex prolactin-releasing response (which
might be established during the first days of lactation)
comparable to the calf-dependent release of oxytocin necessary
for milk let-down (Williamson and Payne 1959; Mahadevan 1966).
Again, such effects are less likely to occur in highly selected
dairy breeds than in undifferentiated general purpose breeds.

Suckling and the health of the calf

Restricted suckling after milking is unlikely to reduce and
may increase the amount of saleable milk from adequately fed
animals. At the same time, the health and growth rate of the
calves are likely to be better if they are fed milk rather than
milk substitutes. Miller (1979) states: "Although calves can
be raised with few deaths on a good milk replacer, often
mortality may be somewhat higher than when whole milk is
fed". Aside from being nutritionally appropriate, milk has
more specific protective properties (reviewed by Bourne 1977 and
Powell et al 1985).

Like colostrum, milk contains antibodies, including important
ones directed specifically against organisms with which the cow
has been infected and which may be present in the particular
local environment. These antibodies are thought to coat the
mucosal surfaces lining the gut and prevent invasion by
ineffective organisms.

Milk also contains cells of several types which are important
for immune responses, including lymphocytes capable of reacting
directly with antigens to which the cow has been sensitized
(Smith and Schultz 1977).

Other non-specific agents are also present, which inhibit the
multiplication of micro-organisms. Although many of these factors
remain in fresh skim milk, drying -especially at high
temperatures- destroys them. So even feeds containing a large
proportion of dried skim milk lack important components.

Preston (1973) summarizes extensive trials involving many
thousands of calves which received milk plus supplementary food,
including concentrates. The mortality of single-suckled calves
was 5.2%; the mortality of those fed with milk from buckets was
12.3%. Intestinal parasites were more common in the bucket-fed
animals (though not as common as in multiple-suckled calves
(Ugarte and Preston 1972)).

Although the temperature of bucket-fed milk, the rate of
drinking and the quantity at each feed can also affect the health
of bucket- fed calves (Stewart 1976; Taylor and Stewart 1976),
these results suggest that the risk of infection is definitely
increased by simply handling the milk. Possibly the milk
antibodies and cells attach to the surface of the bucket, so less
are available to coat the gut mucosa. The hygiene on the Cuban
farms, where these trials took place, may have been less than
ideal but that would apply to most farms in developing countries.

Moreover, when Everitt and Evans (1970) analysed the records
of 2673 calf deaths on experimental farms in New Zealand, they
found that 7.8% of those fed by bucket died, compared to 0.9% of
those suckled (ruminal and abomasal bloat, which accounted for
10% of the deaths, occurred only in bucket-fed calves).

Presumably non-fatal as well as fatal infections also develop
less frequently in suckled calves. Growth rate as well as
mortality data from more recent trials, with various breeds of
cows in several countries, indicate that restricted suckling is
preferable to bucket-feeding (Preston 1983). This confirms
earlier results (Everitt et al 1968; Everitt and Phillips
1971; Smith et al 1973; Paredes et al 1981) which
showed that the growth rate of suckled calves tends to be better
than that of calves fed by bucket.

Since, where feed is adequate, the live-weight gain of beef
calves between 3 months and slaughter is closely correlated with
that from birth to 3 months (Everitt et al 1969),
conditions promoting early rapid growth may have substantial
long-term advantages.

Effect on the cow

In some trials in which suckling enhanced milk production
certain other effects on the cows were observed:

ii) Suckling may prolong anoestrus, the delay being related to
the duration of suckling (Everitt et al 1968; Thomas et
al 1981). Moller (1970) reported that the growth of ovarian
follicles in sucked cows are slower than in machine-milked ones,
so that the first ovulation occurred significantly later.
Moreover, the proportion of animals showing signs of oestrus was
also reduced. Suckling twice a day has a less marked effect than
continuous suckling, which could explain why some other workers
observed no prolongation of anoestrus (Veitia and Simon 1972;
Ugarte and Preston 1972; Fulkerson et al 1978). It should
also be noted that Preston (1983) concludes that although
distinctive signs of oestrus in cows suckled twice daily may be
lacking - making successful AI programmes difficult - these
so-called `silent heats' can often be detected by the bull, and
natural mating generally results in no delay to the next calving.

iii) In many of the trials cows that suckled calves were
reported to suffer less from mastitis than milked ones (Everitt et
al 1968; Veitia and Simon 1972; Preston 1973; Walsh 1974).
Others observed no difference, possibly because the overall
incidence of mastitis was low (Fulkerson et al 1978;
Thomas et al 1981). Preston (1983) concludes from more
recent data that there is indeed a beneficial effect on udder
infection from twice-daily suckling.

iv) In the case of breeds which do not normally let down milk
in the absence of the calf (eg: Bos indicus breeds and
their crosses), it is traditional practice (Preston T R, personal
communication) to stimulate milk flow by very brief suckling
followed by partial (eg: three teats only) milking, after which
the calf is allowed to suck the residual milk.

Conclusions

The data discussed here indicate that the practice of feeding
calves on milk substitutes from an early age is likely to be
economically inappropriate for many resource-poor farmers in a
developing country, especially if a healthy calf is regarded as a
significant asset. Moreover, since the well-fed cow can respond
to the stimulus of suckling after milking by secreting more milk,
early weaning may in fact fail to increase the amount available
for sale. Longer lactations and a reduced risk of mastitis are
additional benefits which may result from restricted suckling and
the reproductive pattern of the cow is likely to be little
affected, provided natural mating is used.

Of special importance in tropical countries is the fact that
many Bos indicus breeds and even their F1 crosses with
European breeds will not let down their milk unless stimulated by
being permitted to suckle their calves briefly prior to hand or
machine milking.

Nevertheless, further trials are needed with specific breeds
of cattle and within the constraints of specific patterns of
farming.

The following particular questions need attention in each
situation:

Does post-milking suckling increase total milk yield?

If it does, how critical is the cow's plane of nutrition
for this response?

For how many weeks should post-milking suckling continue
in order to get (a) maximum saleable milk production and
(b) maximum calf growth and survival?

What are the effects of post-milking suckling for various
numbers of weeks on the duration of both true and
apparent anoestrus?

If for practical reasons it is desired to wean the calf
at 8-12 weeks of age, how will this affect yield or will
some cows or breeds of cows cease lactation due to lack
of stimulus from the calf?

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effect on lactational performance of suckling dairy heifers for
the first eight weeks post-partum. Proceedings of the Australian
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Paredes L, Capriles M, Parra R and Marquez N
1981 The performance of calves reared by restricted suckling
with mothers of high milk production and potential. Tropical
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Peel C J Robinson I B and McGowan A A 1979 Effects
of multiple suckling by dairy heifers for short periods before
and after calving on subsequent milk yields. Australian Journal
of Experimental Agriculture and Animal Husbandry 19:535-538

Stewart J A 1976 Effect of feeding
calves by artificial teats at two drinking rates or by bucket.
Proceedings of the Australian Society for Animal Production
11:265-267

Taylor J W and Stewart J A 1976 The
effect of milk temperature and dilution on liveweight gains and
incidence of diarrhoea in young calves. Proceedings of the
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Thomas G W, Spiker S A and Mickan O 1981 Influence
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